FIGS. 9(a) and 9(b) show a prior art semiconductor device in which a semiconductor chip having bump wirings is mounted on a TAB (tape automated bonding) tape or a printed board. In FIGS. 9(a) and 9(b), reference numeral 1 designates a substrate having a first surface where an active layer 4 is disposed. On the active layer 4, source electrodes 5, gate electrodes 6, and a drain electrode 7 are disposed, and these electrodes 5, 6, and 7 and the active layer 4 form a transistor. Reference numeral 2 designates bump wirings comprising Au, which are disposed corresponding to the respective electrodes 5, 6, and 7, and electrically connected to these electrodes. Reference numeral 8 designates a TAB tape or a printed board having a plurality of through-holes 8a. Wirings 9 are electrically connected to the bump wirings 2 through the through-holes 8a.
In the prior art semiconductor device, in order to achieve the maximum performance of the transistor, the wiring structure using the bump wirings 2 as described above is employed in a flip-chip mounting application. More specifically, the heat radiation effect in the transistor is increased by utilizing heat conduction of the bump wirings 2, and the wiring is laid out along the shortest distance from the electrodes of the transistor with the bump wirings 2, thereby reducing wiring delay.
In this structure, however, cavities are produced on the element surface and when the atmosphere of the element surface changes, the wirings are corroded. Further, ion migration occurs because of the difference in quality of the material between the wiring 9 and the bump wiring 2, so that the wirings are degraded. It is impossible to avoid the above-described problem, and this is a serious problem in view of reliability. Even if the chip shown in FIG. 9(b) is completely covered with resin, it is impossible to perfectly hermetically seal the chip, since adhesion or the like of the resin is limited. Consequently, the problem remains to be solved.
In addition, signal noise from the outside is picked up and noise is generated in peripheral circuits. Therefore, especially when an element comprises GaAs and is utilized in a microwave circuit for high frequency, there is a considerable problem.
As described above, in the prior art semiconductor device, corrosion and degradation of the wirings caused by cavities produced on the element surface cannot be avoided, whereby reliability of the device is not improved. In addition, when the element is utilized in a high-frequency circuit, noise is unfavorably picked up or adversely generated in peripheral circuits.
Japanese Published Patent Application No. Hei. 6-236903 discloses a semiconductor device including a metal layer serving as a ground electrode and disposed around an MMIC (monolithic microwave integrated circuit) chip. In this semiconductor device, noise is picked up from the outside through the metal layer, whereby the above-described problem remains to be solved. Further, Japanese Published Patent Application No. Hei. 3-49246 discloses a semiconductor integrated circuit in which a semiconductor chip is mounted on a substrate mounted on a film carrier through bump electrodes. A sealing portion comprising the same material as the bump electrode is provided on the surface of the semiconductor chip where elements are to be formed, along the circumference of the chip, so that the element forming-surface of the chip is hermetically sealed. In this structure, the elements and the wirings are protected from pollutants, such as moisture and impurity ions. Since this reference concerns a silicon device, however, a measure for preventing noise is not provided. Therefore, an electromagnetic shielding effect sufficient for use as a package of a microwave circuit is not obtained.